The Wicked WorkFlow

A strange bug struck me few days back and I had this idea of making a single workflow interact with multiple applications ( Hosts) at the runtime . Now I might sound a little stupid here while proposing the idea, but yeah I had invested(waisted) two long days just trying to get through this weird idea. Before I drop this proposal, I would be PACIFIED to make people know that this is not possible. A workflow runtime that basically is the engine thta loads the workflow can have one and only one instance inside one application domian. As a workflow needs a Host to sit and execute the loaded workflow, its obvious that there should be a application( windows, web, console) running somewhere to make this engine work. Well, as most of us playing around in this DOTNet world know that one application domain can have just one application thread running at one point in time, its not at all possible to make the workflwo hosted inside one application or for that matter inside one application domain to interact with another application running in some other application domain, untill and unless it is killed from one appl domain and rehosted in some other application domain. So persistance( loading and unloading of workflw from the running workflow runtime) of the workflow though possible in one application domian is not a feasible across application domains. Haveing reached to that conclusion, I am curious to know why such an arhcitecture ?????